<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>定位</title>
    <style>
        html, body {
            margin: 0;
            padding: 0;
            height: 100%;
        }

        .container {
            height: 100%;
            text-align: center;
        }
    </style>
</head>
<body>

<div class="container">

    <button>hello world</button>
</div>
</body>
</html>
